The Severn River, rimmed by forests and bits of history, has lured boaters and dwellers since Capt. John Smith first spotted it nearly 300 years ago, but its popularity could also be its downfall, a state advisory group warned today.

In a new report, the Severn River Local Advisory Board singled out growth as the greatest threat to the estuary, which flows from the middle of Anne Arundel County south into the Chesapeake Bay at Annapolis. To help contain that growth, the group recommended that owners along the river be given property tax credits of up to 100 percent for land donated for conservation easements.

But that proposal was greeted cautiously by county officials. Robert Agee, chief aide to County Executive James Lighthizer, said it could be unfair to owners of small properties who have no land to donate.

The group also called for changes in county laws and regulations governing sediment control, storm water management, waste water treatment and development.

Erosion and sedimentation have already damaged oyster beds and built sandbars that are difficult for boaters to navigate, as the shores continue to develop, said Clifford A. Falkenau, chairman of the 12-member citizens group. Only the Severn Run environmental area at the river's headwaters remains wild.

"We recognize you're going to have continued development, but we want it in a controlled manner," Falkenau said.

Other recommended changes include on-site reviews of proposed subdivisions (rather than relying on maps, which the group said could be misleading); clustering development to avoid disturbing natural terrain; banning recreational sites within flood plains; reducing the amount of chemicals used in waste-water treatment, and greater use of septic and on-site sewer systems.

The report also lists various ways, including paving roads with porous pavements and keeping grass at higher levels higher, to reduce storm water runoff and erosion.

Lighthizer said the recommendations generally fall in line with efforts already under way in his administration. He added that he plans to submit legislation to the County Council by October that would tighten county sediment control and storm water management ordinances.

Torrey C. Brown, secretary of the Maryland Department of Natural Resources, who presented the report to Lighthizer, hailed the comprehensiveness of the report as a model of what the state would like to see done for all the watersheds of the Chesapeake Bay. Gov. Harry Hughes has made restoration of the bay, which has declined in quality and aquatic life, a top priority.

The Severn River report is the second to be issued under Maryland's Wild and Scenic Rivers Act.